Current guidance says patients must undertake three lateral flow tests (LTF) and register the results on the self-report portal before surgery can take place.
But the South Eastern Health Trust said that during one recent 12-day period, 76 patients turned up at hospital without completing the required tests.
This can lead to a delay of six hours before they can be admitted to hospital.
At the height of the coronavirus pandemic, patients were asked to attend for a PCR Covid test, 72 hours before surgery and also to self-isolate until they were admitted for their surgical procedure.
The testing guidance has been amended to three LFT tests but the trust said community transmission of Covid remains high.
Chris Allam, assistant director of elective surgery and radiology services, said: “The testing procedure before surgery has now been replaced with a set of three self-test lateral flow tests which must be undertaken and the results registered on the government self-report portal (www.gov.uk) prior to admission for surgery.
“Instructions on how to administer and register an LFT are provided to every patient when they are booked for surgery.
“We understand that for some this is difficult and we have alternative processes in place for these patients if they inform us when agreeing the date and time of their elective procedure.
“These processes can be either agreed verbally, if patients are contacted directly, or by telephoning the booking team on the number provided on the confirmation appointment letter.
“Over a recent 12-day period, 76 patients turned up for their procedures without carrying out the necessary LFT testing at home.
“This equates to approximately seven patients per day and almost six hours of additional time required to carry out testing before admission.
“It is essential that patients have taken all three LFT tests that have been provided to them, as well as uploading their results before their planned surgery date to ensure their operation can go ahead without delay.
“It’s emerged some patients have been bringing their unused testing kits with them to their surgery appointment, staff must then prioritise this patient and assist them to take an LFT test on arrival before they can be admitted to the unit.
“This has caused delays and the loss of theatre slots, impacting on waiting times for surgery due to staff having to wait for around 30 minutes for the test result before being able to start the admission process.
“Staff often have to be redeployed to facilitate the patient taking an LFT test, which can have an impact on their duties. If the patient tests positive, it also increases the risk of infection to other patients, staff and visitors.
“This new testing guidance allows us to fill appointments that become vacant when someone tests positive prior to their procedure and it also ensures elective surgeries go ahead as planned.”